Introduction to Genetics and Evolution is a college-level class being offered simultaneously to new students at Duke University. The course gives interested people a very basic overview of some principles behind these very fundamental areas of biology. We often hear about new "genome sequences," commercial kits that can tell you about your ancestry (including pre-human) from your DNA or disease predispositions, debates about the truth of evolution, why animals behave the way they do, and how people found "genetic evidence for natural selection." This course provides the basic biology you need to understand all of these issues better, tries to clarify some misconceptions, and tries to prepare students for future, more advanced coursework in Biology (and especially evolutionary genetics). No prior coursework is assumed.

IW

Excellent course. Would recommend it to anyone who wants to delve in the subject matter. Wonderful instructor and interesting lecture videos. One of the best courses I have taken in Coursera.

VL

Jan 17, 2017

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I really enjoyed the classes and the supplemental materials available. I loved how the lessons were taught and explained by Dr. Mohamed Noor and I really enjoyed the content of the classes.

À partir de la leçon

Evidence for Evolution

This module discusses the definition of the word "evolution" in a biological context, evidence for the truth of evolution and common ancestry of species, and public thoughts and misconceptions about biological evolution. This module is optional and will not be included in the course assessments. There are not class discussion forums for this section, as we feel such discussion can happen on other, non-course-related, sites on this topic (of which there are a great many on the internet).

Enseigné par

Dr. Mohamed Noor

Earl D. McLean Professor and Chair,

Transcription

We're here today with Professor Jerry Coyne from the University of Chicago, author of the best-selling book Why Evolution is True. And we have some questions for him. Thank you for joining us Jerry. >> My pleasure. Hey out there. >> [LAUGH] So what first prompted you to study evolutionary biology? Well, it was, as often the case, a charismatic professor. In fact, probably one that you knew too. Actually it's a combination of them. My intro bio came sure my very first day of class. 8 o'clock on Monday my first day of college was a guy named Jack Brooks at William and Mary and he was a herpetologist with evolutionary interests. And he was such an inspiring lecturer that he got me all juiced up about studying evolution. To the extent that I wanted to take genetics and evolution my second year instead of my third year. Which was normal. So he let me do that and I fell into the spell of another charismatic professor one you know of. Bruce Grant who was also very inspiring. Bruce studied the evolution. In the fruit flies, in particular, just in speciation. And that was it for me. I was hooked on studying flies because they could do experiments on them and they have a short life cycle. And the excitement that taught evolution was conveyed to me. That shows, for one thing, the importance of teachers, and- >> Absolutely. >> On people's lives. So many people have chosen their careers, including me, because of charismatic teachers. >> Absolutely. So why did you decide to write the book, Why Evolution is True. >> Well the book actually grew out of my lectures. When I first started lecturing, God it was almost thirty years ago at the University of Maryland, I was assigned to do the Introductory of Evolution course. And so when I went back to look at the textbooks on evolution, I had to teach it in the past. I found there's a real difference between the textbooks that were used. Say in the 1920s and 30s when evolution wasn't so widely accepted. Especially natural selection. And the textbooks that are used now in particular the earlier textbooks have long, long sections on why evolution is true. Or why we accept evolution. The fossil record. Embryology by the vestigial organs the modern textbooks just assumed that you already knew that evidence and that we you know once you already knew it. Just like when you take chemistry they already assume you know that atoms exist. >> Yes. >> And then it just went on from there, you start with population genetics Now the history of life etc. But the fact is that most kids coming into Introductory Biology or Molecular Evolution don't know the evidence of evolution. They don't know how strong it is. They don't know the areas for just arrived and how they all draw together and how diverse those areas are arranging from natural history to molecular biology. And I wanted the students to know that. And one of the main reasons I want them to know that is because there's such an anti-evolution sentiment in this country. 40% of Americans don't accept evolution and if you count those that don't accept the scientific view of evolution, it goes up to about 70%. >> Wow. >> There's about 30% think that evolution is driven by spiritual or supernatural forces. So there's this huge opposition to evolution in this country and I thought well. Maybe that opposition rests at least partly on ignorance. That people just don't know that there is so much evidence for it, and if I was to put it down in a simple, easy to digest form for the general public, that maybe this opposition would go away. I think that was probably now, if I am not mistaken idea but that was my idea. And I also wanted to put it down because I have been teaching all of this stuff to the kids. I decided I was going to start my evolution class with two to three hours of the evidence for evolution. For several reasons. First of all they need to know it. If they need to know anything about evolution going out into the world. They have to remember what the evidence says. Second of all, because of this pervasive anti-evolution sentiment, which is basically anti-science, in America. And third of all, presenting evolution against the alternative, which happens to be creationism. In this country, it is a way of teaching how science is done, and having way different interpretations of the same observations. It's a perfect lesson in how to learn science, so for those reasons I thought I would not only teach the students in my introductory course the stuff first. But also write a popular book about it. I'm not sure how much influence that accounted changing people's minds about evolution. There's a lot of resistance turns out to be based not on ignorance but on simple most genesis based on the fact that it seems to contravene people's religious beliefs. >> So what do you find, this is a two part question. What do you find to be the most interesting observation supporting the truth of evolution? And the most exciting subdiscipline or area of research within evolutionary biology? And why on both? >> You know, and they said there was a lot of different areas that come to bear on evolution. >> Absolutely. >> A fossil record is the most obvious one, but there's also, as my book describes, embryology, the way the organisms develop. The existence of non-functional vestigial organs. Molecular biology, the hierarchical arrangement of species in the tree of life and biogeography. And of those I guess when I was writing the book, the one I found most interesting because I didn't know so much about it was biogeography. That the distribution of plants and animals on this planet can be explained only under Darwin's theory of evolution, dispersal and subsequent evolution. And it was so important to Darwin that he devoted two chapters of his book to it and ever since then, more and more evidence has been accumulating. Like we found fossil marsupials on Australia, which supports the notion that they move to Australia from South America and Antarctica. Sorry, we found the fossils in Antarctica and then Australia. They used to be connected together. They evolved in South America and now we find marsupials mostly in Australia. Well if that happened they would have had to get to Australia and to do that they would have had to go through Antarctica. Well just in the last ten years they finally found fossils of marsupials in Australia. So all of this evidence from geography comes together to support evolution and it's very powerful and pretty convincing and to me I was largely ignorant about it I found it very interesting. It's also one of the ones that I'm interested in is almost impossible to refute under any ulterior theory especially creationists. In terms of what I find personally most interesting when I research on it is of course what I work on and what you work on which is speciation the origin of human species. I guess the reason I like it, well first of all, Bruce Grant, my undergraduate mentor and yours. He was interested in that, but I also became convinced that was one of the last great outstanding questions in evolutionary biology because Darwin didn't get it right. In the origin he got a lot right but he didn't understand really how we have these distinct entities called species and actually there's no inherent reason why nature should come to use in these discrete packages called species. Why we wouldn't have a continuum of words instead of species like robins and starlings and pigeons. Understanding why that's so, and how those discrete groups come into being, was a question that, Darwin didn't answer it. It started being proposed again in the 30s and 40s. And the genetic basis for the formation of these species really did not come to the fore until about the time I got interested in it in the 80s or so. And it's because it's an important question. I mean, one of the most important questions in biology is why does nature come in these discrete packages we call species? And I just wanted to be able to make the contribution to that. >> That's great. So how do you think life first began? And have there been any good studies explaining this or at least putting forth compelling hypothesis? >> Well, there's compelling hypothesis. I mean, if you wanna read, there's a lot of compelling hypothesis [LAUGH] >> [LAUGH] >> There's just one question that we don't understand, that doesn't mean that, I mean there's a lot of science questions that we don't understand. Like how, is there more than one universe and stuff. It doesn't mean the explanation And something supernatural. It just means that we- it's very hard to study the origin of life because we weren't there when it happened. Plus the original creatures that evolved were probably proto-molecules, like amino acids or nucleotides, which we now think. And they didn't fossilize. So we weren't there to see it, and we don't have any fossil traces. So, how do we figure out how it started? That is hard. There is a book called Genesis, which is just the word Genesis with an asterisk in between each letter, which lays out all the various hypotheses of how life began, started as depositions of organic matter on clay, through crystallization, their most prominent going hypothesis now is that life started as sort of an RNA-like molecule. And the reason we think that is because RNA is both something that can replicate but something that can also have enzymatic activity. And the whole problem of the origin of life is, how do we get DNA or nucleotides thing, that is both self replicating and can produce proteins? When, to replicate you have to have the proteins in the first place, and in order to get the proteins, you have to have the nucleotide sequences. So you have this chicken and egg problem, and that is partially answered by the fact that RNA, unlike DNA, can both replicate itself and has its own enzymatic properties. Now we don't know if that's right or not. And I don't know if we'll ever really know how life began. We know it only began once. Because of certain fundamental similarities of organisms. But, I think that in the next 50 years we'll be able to replicate the origin of life. Or, not replicate it, but get the origin of life in the laboratory, under proto-life conditions. Those that are obtained at the beginning of life about 3.5 billion years ago. And that will answer the question that it couldn't have occurred naturally. That doesn't tell us how it did occur naturally. >> Yeah. >> And that question may forever elude us. But it will at least eliminate the counter objection, because life couldn't have originated naturally, it must have been done by God or some other supernatural agent. But, you know, I mean, this is early days. This is a hard question. It's only one that's been properly investigated in the last 20 or 30 years. It's gonna take a while. To get sort of forever, so. >> Yeah, it makes sense. So the classic example of an observation that's said to refute, or that's said that could refute evolution is, quote, fossil rabbits in the Precambrian. Barring that extreme example, what else do you think could provide evidence against evolution and the common ancestry of species? Well there's a lot of them. The one you said is the most common. Fossils in the wrong place. If we found a human fossil 400 million years ago, well, I mean that would cast severe doubt on it. You'd have to find more than one. Cuz you could say, well, it was some kind of bizarre artifact. Some human fell down in through the sediments >> [LAUGH] >> Through a crack in the Earth. I have a whole list of them. Adaptations in one species, for example, that are good only for members of another species. Darwinism says, you cannot evolve something in a species if it is not useful for the individuals for that species. So if you find something, like, for example, nipples [LAUGH] on some mammal that can only suckle members of another species, that would be strong evidence against evolution. We don't see that, cuz none of this stuff I'm gonna tell you is evidence against evolution, or ever been observed. That's one reason we think evolution is true. If we didn't see genetic variations in a species, cuz to get evolution, you have to have genetic variation. Then, if we could not take species then show that through artificial selection that they had genetic variation, that would cast your doubt around the ability at least natural selection, or any process that causes variation. But, find again that every species has ample genetic variation. If we see any adaptations that could not have evolved in a step by step process, that's through gradual change, and in complex adaptations, which bears on a question you might ask later about intelligent design. That would count against Darwinism. And if we saw, I mean there's a lot. I'll just give one more. If we saw strong discords between the relationships between organisms, that we see from their DNA sequences and the relationships we see from their morphology, then that would cast severe doubt on evolution. For example, show why using that the DNA sequences of whales, in general were much more similar to those of fish than they were to any other mammal. That would cause some problems for evolution. But, of course, if you the phylogeny based on DNA, you see whales fit right in there with other mammals and fish are over here somewhere. So, I have a list when I give a talk of a dozen observations that could refute modern evolutionary biology. It's not a watertight theory in the sense that there's nothing that could possibly refute. But none of these observations have even been made. That's one reason why we think Darwinism is true. It's had, as I say in the book, it's had a million chances to be wrong, but it's always come out right. And when that happens we consider something to be true in the scientific sense. >> Okay, that's great. Well as you've alluded, I have a couple, the next couple of questions, the next three here are looking at some of the arguments that people pose who are hostile to evolution. So, this next one's a little bit long. It says, some evolutionary biologists come across as particularly hostile and condescending to alternative points of view, insisting that everything is explained by evolution and common ancestry, and even considering anything besides reflects ignorance or stubbornness. In contrast, advocates for Intelligent Design agree that evolution happens, but suggest that we should be open to additional explanations rather than a singular one. How did evolutionary biologists justify their certitude in a singular explanation for all of life? And relatedly, why do they come across as so condescending to those who even consider alternatives? >> Well, I suppose that's not like the consensus of the class. Maybe it is, that scientists are condescending, evolutionary biologists. I don't think we all are. That said, I think there is a bit of truth in that characterization, but let me put that off for a second. I wanna take issue with the idea that evolutionary biologists think that everything has to be explained by evolution, because I don't think that's true. For example, there's culture. At least for humans, there is culture and a lot of the aspects of human culture cannot be explained by evolution, because they change so fast. Why there's Coke and Pepsi and why we have Bach and Beethoven. How we build submarines. Those are all within our capabilities as biologically evolved organisms. But those phenomena and a number of cultural phenomena, like for example, the institution of religion. Music, dancing, things like that, literature. All of that are probably cultural phenomena that--well they have to be consonant with what our genes enable us to do, they're not evolved. We don't have genes, I don't think, for writing literature. I don't think we have genes for believing in God. I think that's a cultural institution. So, no, not everything comes from evolution. Although a lot of our biological characteristics do. And in animals that don't have culture, like protozoans, for example, or plants, a lot of their features do come from evolution. Okay, so I'm just saying that very few evolutionary biologists think, in fact, none that I know of, think that evolution explains everything in humans. Because we have this culture which supersedes or, may supersedes evolution. In terms of the fact that people reject intelligent design, and there may be additional explanations besides the natural materialistic one of evolution, that there might be an intelligent designer. That facilitates evolution. That's the view called sort of theistic evolution, of which Intelligent Design is one view. And they say, well, why reject that out of hand? Well, some scientists do. In fact that's the reason why the courts reject it. Because they consider Creationism as a form of religion. Which it really is. It's religiously motivated. But I don't rule it out of court. I mean I say Let's consider all explanations for biological phenomena and see which ones work. So I'm one of the few scientists, I guess, that say, let's consider the supernatural. We can test it. I mean, there have been tests of whether the supernatural works in biology. One of these famous ones is intercessory prayer, where there have been several studies where religious groups prayed for people that where in the hospital. They were having operations, and there were control groups people weren't prayed for or prayed for wrongly, etc. And it didn't work. So and if you have the view, as the American Indians did, that dancing, doing particular dances would bring rain, well, that's an assertion of the supernatural that's also testable. You could see whether the dancing would cause the rain. You could have a control where the dances aren't done right. You could have no dances, etc. So if you have a formal religion or a belief in supernatural that claims that the supernatural does affect the real world. And most religious people do believe that. Then, at least, in principle, that becomes something that can become empirically testable. You can see whether spiritual healing works, whether prayer works, blah, blah, blah. And none of those tests have ever worked. And you can see whether the intelligent design assertion, which is that there are features of biological organisms that could not have evolved, must have been created by an intelligent agent. You can also see whether those things are worth considering. And I think that you should consider that alternative because a lot of people believe it, and test it. The problem is the prayer studies and the rain dancing studies, well, there haven't been any rain dancing studies. >> [LAUGH] >> $1000, they wouldn't work. But well, like studies of ancestry prayer and spiritual healing, intelligent design arguments, I reject them because simply they haven't worked. And so they're bad science. And we don't know of any feature of an organism that in principle could not have evolved in an adaptive way from precursors. It's a God of the gaps argument. Just because we don't know exactly how something evolved, we can't automatically say it must have been designed. And now we're starting to find that some of these features, and the flagella and blood clotting are the classic examples used by intelligent design people. We're starting to find out ways in which they could have indeed involved in a stepwise fashion, and that they're not so-called irreducibly complex features after all. So I don't rule out supernatural explanations. I think that science should consider them. I think science has considered them. I mean Newton, sorry Kepler and other early astronomers thought that God was responsible for certain planetary motions. And so then it was later shown that you didn't need God to do that. And the whole history of science has been one in which supernatural explanations have been continuously discarded, one after the other. So now the situation is we don't really consider them, not because they're not worth considering, but because they've never shown themselves to be useful in understanding any phenomenon. But I'm still willing to consider them. If something happened, if prayer worked, but it was only Jewish prayers, or Catholic prayers. Or if telepathy seemed to work or spiritual healing seemed to work, then I for one would be willing to consider the supernatural. But so far, there's been no reason to do that. >> Okay, that's great, thank you. So this next one's kind of a long question. In your book and on your blog, you present many examples of cases that are not easily explained by design that are consistent with long-term evolution. For example, you mentioned that the recurrent pharyngeal nerve is an example of inefficient design. The appendix is an example of a vestigial organ, and vitamin C producing genes as dead in primates. If we take these examples at face value, they all seem like relics of an evolutionary process. However, it's possible that at least some and maybe many of these examples have explanations that have not yet been found. For example, as you probably know, Dr. William Parker at Duke University has said quote, the abundance of circumstantial evidence makes a strong case for the role of the appendix as a place where the good bacteria can live safe and undisturbed until they're needed. Such a function may outweigh the risk of appendicitis. Others have argued that the recurrent laryngeal nerve innervates tissues in the chest in addition to the larynx. Thus making it perhaps somewhat or very efficient and many supposed dead genes are transcribed and have functions discovered much later as shown with the N-CODE project recently. As such, some or many of these examples are vestiges or bad design could be disproven with future studies. How do you feel about this and the evidence [INAUDIBLE]? >> That is a long question. There's three examples specifically mentioned in there. I'll try to answer as briefly as I can. I mean, there's a fallacious notion at work here, which is the vestigial organs can't be useful for anything. And we've got others that don't believe that. We believe that vestigial organs are features of an organism that can be explained only by positing that they had a different function in a common ancestor. That doesn't mean that those organs cannot be co-opted for something else in a descendant. So if you find that an organ that's said to be vestigial actually has some function, then that doesn't mean that evolution is wrong. [LAUGH] And let me give you an example. So the wing of an ostrich, I mean, ostrich is like big feathers versus the [INAUDIBLE] evolved. We know this from molecular work. And the he thought from organisms that had wings with which they could fly, so do penguins. And in the case of penguins those wings that used to be used for flying in the air in their ancestors are now used for flying in the water. Does that mean that penguins that the wings are evolved de novo are the result of creationism? Know that they're leftover remnants of the ancestors of penguins that now have a new function, which is to propel them through the water. The ostrich has wings. So ostriches can't fly because their wings are too small. But they still use them in a way that you could consider of them. In particular if you ever get chased by an ostrich, and I have been, they put their wings out to make themselves bigger and scarier. But they also use the wings to shade their chicks in the African sun. They spread them out over the chicks. So you could say okay they have a function. They're not vestigial. But really, I mean why does an ostrich have these wings in the first place? Because we know they evolved from birds of flight. To give a more extreme example, look at the kiwi which is another flightless bird found in New Zealand. It has wings that are like that big that are hidden under these hairy like feathers. And they have no known function at all. And they can't do anything. So, [LAUGH] the reasonable thing is, and if you look at these wings and dissect them, you'll see they have little sort of bones in them that are of course the bones of flying birds. We have the whole gamut in there from penguin wings, which are functional to flying under water. Ostrich wings, which you can't really fly anywhere, but you could use them in an adaptive way, to the kiwi, where they're just no use at all. It's just, and they all have the same bones in them. It's hard to see that that says anything except that those birds had common, flying ancestors. The alternative is there is a creator that created all of these wings using exactly the same bones and to do different things in different birds. And in the kiwi, they're there, they don't do anything, okay? [LAUGH] In terms of the appendix, yeah, there is a residual, probably, immunological, or health function, in the appendix. We think that there's some tissue in there that's useful in the immune system. And they may harbor some useful bacteria. Like, when we get rid of our gut bacteria through antibiotics, they may be replenished by bacteria that are hidden in the appendix. But, remember the appendix evolved before we had antibiotics. So, [LAUGH] you gotta remember that the appendix evolved its vestigiality not now when have doctors that can take it out when it's inflamed. But way back in our ancestors on the savanna, three or four million years ago, when it's estimated that between 15% of people or more got appendicitis. And when you got appendicitis on the savanna, you were dead basically. There were no doctors to take out an inflamed appendix. So there was a huge cost Of having an appendix based at the time and that's why it's gotten smaller and smaller and smaller. Now it's probably gonna stay because now there's no problem with having one. If it gets inflamed, at least in most places in the world, doctors take it out. But if we look at our relatives, like plant-eating things or even the orangutan, the appendix serves as a large sack in which plant material ferments and breaks down, before it goes back into the intestine. And it's clear that that's where our appendix came from. It may have a residual function, but it's hard for me to believe that this tiny immune function it has, or replenishment of bacteria from having them wiped out of your gut by antibiotics which is something that didn't happen when the appendix evolved, that was huge mortality deficit that occurred from having an appendix on the savannah. So yeah, it's not a good thing to have. It's not there because it's in general good for us, at least it was not good for our ancestors. It's very difficult to make a case that having an appendix was good and that's why it's getting smaller because it's bad. Now in terms of the dead genes in the ENCODE project. I had to look this sort of up this morning because there's been seven papers in nature in the past couple weeks on the ENCODE project, and it doesn't really say that dead genes are really functional. Classic examples of the dead genes I give in my book are the last gene in the process of synthesizing vitamin C, which in most mammals is useful. They make vitamin C in their metabolic pathway. We don't cuz the last step in the pathway is blocked. The gene that makes that last step from the precursor of vitamin C to vitamin C has a mutation which makes the enzyme inactive and so we can't make vitamin C. That's why we have to get it in our diet. That's why sailors got scurvy on trips. They had to eat limes to get the vitamin C etc., so that gene's dead. You can see that the gene is alive, it actually does not have that mutation in some of our relatives. We happen to have the same dead gene as gorillas by the way and a little bit of a different one from orangutans, which testifies to the fact that the gene was killed in one of our primate ancestors. So the supposition is well, maybe the gene is still useful because even though it doesn't make protein, the RNA transcript of that gene might have some other use. And that's what the ENCODE project is starting to tell us for a lot of, and not necessarily for the vitamin C gene. From a lot of parts of the gene that we thought were nonfunctional actually produce RNA transcripts, they conserve and regulate other genes, and that may be true for the dead vitamin C gene. I don't know. Even if that were true, they would not say that that thing is dead is evidence for, that dead gene is evidence for evolution because it is. I'm not sure we know where that gene makes an RNA transcript but we know for bloody well sure it does not make protein. It was there to make the enzyme that converted one thing to another. So what has happened if it makes a transcript that is useful for some other thing, is the same thing that happened at birth. Something that was eliminated by evolution for one purpose is collected for another purpose. The only way you can explain that we have a gene that codes for enzyme that, in other species, actually produces an enzyme that makes the vitamin C, but we don't, is to positively evolved from ancestors in which that gene was active. There's no other way around that, no matter what the gene does now. And it's the same for every dead gene that I talk about it my book. Not only the vitamin C gene, but the olfaction genes that were useful in our smelling in our ancestors and are no longer useful for us because we're a visual species and an auditory one rather than an olfactory one. And the genes that make yolk protein in our relatives which are birds and reptiles. They don't operate in humans. They're still there and they're dead. They don't produce a protein. They may produce an RNA transcript that could be co-opted for something else. But the reason those genes were there in the first place is they produced protein that made yolk for the embryo. So the ENCODE project, to me, is a very interesting result but it doesn't say anything about denying evolution, because the genes that we thought were dead actually do something else. That all this apprehension that vestigial characteristics in order to prove evolution can't do anything at all and that's not true. Vestigial characteristics proves evolution have to been explained only by the central man ancestor, but they could well have been used by evolution to do something new after they become useless for the first function. So that would be my explanation. >> That's great. The last question that was submitted is can you please come up close to the screen and wiggle your ears [LAUGH]? >> [INAUDIBLE] ear wiggling is a vestigial trait and believe me, it can't be useful for anything. >> [LAUGH] >> In evolution for a trait to be useful is it's adaptive. And for it to be adaptive, it has to increase your reproduction. And I can't see any way that wiggling your ears can increase your reproduction. It certainly never helped me acquire any mates. >> [LAUGH] >> It's there because we inherited the vestigial traits, the muscles that our ancestors. If you look at their cat and their dog, they can move their ears around to locate sounds. We don't really do that. We don't need to do that because we're mostly a visually-oriented species, but we still, not everybody has these. I mean, that's another sign of a vestigial trait. And everybody has these three muscles in fully-developed form that enable them to wiggle their ears. I have them too. So when I wiggle my ears, I'm just showing you there's this vestigial trait that remains in some humans but is of no conceivable use, at least in terms of facilitating reproduction. And so I'll try to get up to the screen and wiggle them. I don't know, can you see that okay? I haven't started wiggling yet. I'm just wondering if you can- >> Yeah. I can see your ear. >> All right, here we go. >> Yeah. Looks great. [LAUGH] >> My visual demonstration of evolution for you. >> There you go. Well, Dr. Coyne, thank you very much for joining us and we really appreciate your time and your efforts. And thank you for a great book, too. >> Hey Mike, pleasure. And to the students out there I say learn evolution and study hard. >> Excellent, take care. >> Bye.